1. Technical Field of the Invention
The present invention relates to water-dispersible compositions based on at least one rare earth, as well as the procedure for the preparation thereof.
This invention also relates to colloidal suspensions produced from such compositions and to catalysts manufactured therefrom.
2. Description of the Prior Art
It is known to this art that catalysts can be in the form of carriers, such as a heat-resistant ceramic unitary shaped article or monolith, or a metallic substrate, coated with a coating typically comprising a material that provides a porous layer, such as alumina, titanium, or zirconia, and catalytically active elements, such as precious metals and other elements, for example metallic oxides and, more especially, rare earth oxides, in particular cerium oxide or zirconium oxide, which may impart a catalytic function itself and/or a carrier function for precious metals. This coating is typically referred to as a "washcoat."
To prepare this coating, suspensions or colloidal solutions of the other metallic elements, such as cerium or zirconium oxide, are, for example, mixed with alumina. The quality of the coating prepared will be dependent, in particular, on the amount of the mixture thus formed, and the quality of such mixture will increase as readily dispersible materials become available, namely, materials that can, when dispersed in water, provide suspensions that are sufficiently stable and concentrated to be used for the formulation of such mixtures.
Serious need thus exists in this art for dispersible compositions that can be used to prepare catalysts.
Furthermore, an increasingly pronounced trend also exists in this art to incorporate elements in catalytic compositions, no longer in separate, uncombined form, but, to the contrary, directly in the form of solid solutions thereof. This is the case most notably with respect to cerium and zirconium. In this instance also, there is a great need for products that comprise solid solutions.